Process for generation of chlorine dioxide



Nov. 2l, 1950 w. s. HUTcHlNsoN 2,530,468

PROCESS FOR GENERATION OF CHLORINE DIXIDE e Filed oct. 21, 1947 No2 ToSTORAGE 0R mscHARGgw 1 clo2a AlR Patented Nov. 21, 1950 PROCESS FORGENERATION OF CHLORINE DIOXIDE Willis S. Hutchinson, St. Paul, Minn.,assigner to Matheson Chemical Corporation, a corporation of VirginiaApplication October 21, 1947, Serial No. 781,157

6 Claims. (Cl. 23--152) This invention relates to the generation ofchlorine dioxide by reacting nitrogen peroxide with a chlorite.

In my copending application Ser. No. 544,646, led July 12, 1944, nowPatent No. 2,475,285, I have described and claimed a process for thegeneration of chlorine dioxide whereby nitrogen peroxide is caused toreact with an alkali or alkaline earth metal chlorite, the nitrogenperoxide advantageously being mixed with an inert gas, air, forinstance, prior to the contact with the chlorite, whereby chlorinedioxide, free from elemental chlorine and in safe concentrations, may beeconomically produced. My present invention constitutes an improvementin the process of my said copending application and provides an improvedcyclic process whereby nitrogen peroxide is recovered from the residualsalts and is repeatedly used for the generation of additional chlorinedioxide.

According to the process of my copending application, the nitrogenperoxide, diluted with air or other inert gas, as previously noted, ispassed in contact with the chlorite, for instance, sodium chlorite, inilaked or granular form resulting in the reaction of the nitrogenperoxide with the chlorite to form chlorine dioxide gas and sodiumnitrite. The nitrogen peroxide for use in the process is continuouslysupplied to the system, for instance, by passing air through a field-the initial charge of nitrogen peroxide is introduced. A

My improved process accordingly comprises a cyclic operation composed ofa plurality of dependent, cooperating steps comprising the reacting ofthe nitrogen peroxide with the chlorite to form chlorine dioxide and thecorresponding -nitrite, the recovery of nitrogen peroxide from thenitrite and the reacting of the liberated nitrogen peroxide with furtherchlorite to generate additional chlorine dioxide.

The recovery of nitrogen peroxide from the nitrite is, with advantage,effected, in accordance with my present invention, by reacting an acid,advantageously a relatively non-volatile acid,

sulfuric acid, for instance, with the nitrite constituting the residualsalt from the chlorine dioxide generation step. The reaction of the acidwith the nitrite results in the generation of nitrous gases composed ofNO2 and NO in equal molar proportions. Simultaneously with, orsubsequent to, the generation of the nitrous gases, air or otherinexpensive source of oxygen, is admixed with the nitrous gasesresulting in the conversion of the nitric oxide, NO,`to NO2.k Theresulting mixture of NO2 and air is thenreturned to the chlorine dioxidegenerating step.

The chemical reactions involved in my cyclic process, when sodiumchlorite and sulfuric acid, for instance, are used, appear to be asfollows:

In converting a chlorite to chlorine dioxide lt has usually beennecessary to provide an oxidiz'- ing agent which serves to increase thevalence of chlorine from 3 in the chlorite to 4 in the chlorine dioxide.So far as I am aware, it has not previously been possible to useatmospheric oxygen, or other cheap sources of gaseous oxygen, for thispurpose. However, by the use of the nitrous gases as an intermediary, inaccordance with my present process, I am enabled continuously togenerate chlorine dioxide from the chlorite, once the process is inoperation, with the addition of little or no oxidizing agent other thanair, or other cheap sources of gaseous oxygen.

In place of sulfuric acid, other relatively nonvolatile acids whichreact with the nitrite to produce NO2 may be used, for instance, syrupyphosphoric acid, or other somewhat more dilute phosphoric acid may beused. Also concentrated nitric acid, or somewhat more dilute nitric acidis usually sufficiently non-volatile for use in my process. The acidused should be relatively nonvolatile so as to avoid contamination ofthe resultant nitrous oxide gases with excessive acid vapors.

Particularly desirable results are obtained by the use of sulfuric acidbecause of its relative cheapness and its effectiveness. Sulfuric acidin concentrations as low as 50% is usually effective but generally it ismore advantageous to use sulfuric acid of 85% concentration or higher,up to a concentration of say 98%.

Sodium chlorite is especially desirable and effective in my processbecause of its commercial availability and because the residual saltsformed hereirom are highly soluble in water. However,

the chlorites of other alkali and alkaline earth metals may be used, forinstance, potassium chlorite and calcium chlorite.

As previously noted, it is usually desirable to generate the chlorinedioxide in relatively low concentrations ini an inert gas, f'orinstance, air, and this iselectively accomplished byV diluting the NO2with air, prior to its reaction with the chlorite. However, other inertgases may be used for this purpose, for instance,. nitrogen, argon, ormixtures of gases inert with respect to theA nitrogen peroxide, thechlorite and the chlorine dioxide. l

My cyclic process is, with advantage, carried out in apparatuscomprising three separate chambers advantageously composedn ofvertically' elongated towers or tubes, one chamber. being used as thechlorine dioxide generator inthe rst step of my process, a secondchamber being used for" the recovery of the`nitrogen`- peroxide fromthenitrite, while a third chamber is being cleaned, dried and rechargedwith fresh chlorite.

Itwilli bev understoodl that my present" invention is not restrictedwith'- respectv to the type'of apparatus in which the process is carriedout. However, the process will be further described and illustratedwithV reference to the accanipanying drawing'which representsconventionally and somewhat' diagrammatically, apparatus such as justdescribed.

vrIn the drawing, three substantiallyA identical lverticallyelongatedchambers are indicated by the' reference numerals I, 2* and;3;, respectively, each provided near its-upperl end withv an opening 4through which'thechamber. may be charged with theY chlorite, sodium;chlorite; for,v instance, in granular" or powdered formrand: adapted tobe closed duringoperation.. A. similar opening 5, also adapted to beclosed during operation, is'

provided near the lower end of eachy chamber.l

In operation, chamber I, for instance', is lled with the solid"chlorite, preferably mixed with an inert material; adapted' torfacilitate the passage of gases therethrough, forexample, porcelain Berlsaddlesbrokenglass tubingor the like, the charge being supportedbythe'perforat'ed support 6. In starting the operation, nitrogen peroxidediluted with any inert gas, air for instance, ispassed to the systemthrough manifold line I and, from thence, through valved connection 8intov the lower end` of: the generating chamber l and passes upwardlythrough' the bed of chlorite in` the chamber. The nitrogen peroxidereacts with the chloritel to generate chlorine dioxide which passes offfrom theupperendof the chamber'through valved connection` Ef andmanifold" IIJ, in safe concentration in the air, or, other: inert gas tothe point of use, the air being premixed with the nitrogen peroxide or'separately introduced into thechamber'through manifold II andvalvedconnection I2;

Y 'Ihegeneration` ofchloringdioxide in chamber I is continued until: thechlorite has been substantially completely converted to the nitrite. Thepassage of nitrogen peroxide to chamber` I is then discontinued andinstead is passed into the lower end of chamber 2, which' haspreviously'been charged with chlorite.

The valve in connections 8 and 9 havingr been closed, sulfuric acid, orother relatively strong, non-volatile acids, is then passed into thetopof chamber I' through' manifold I3" and valvedconnection' I4.Simultaneously therewiths air is passed upwardly through the chamber.

vresultant nitrogen peroxide in admixture with air passes from the upperend of the chamber through valved connection I5 and manifold I6 tostorage or elseY through line I1 into manifold T and 'from thencethrough the valved connection 8 of 'the chamber then being used forchlorine dioxide generation. A nitrogen peroxide drier I8 of known typeis, with advantage interposed in line I'I for the removal of anymoisture or entrained acid present in the gas.

'Ifhe'rate of addition of the acid is; with advantage, regulatedfinsuch. a way as to#- generate nitrogen peroxide at a convenient rate forits direct introduction into the chlorine dioxide generating chamber orchambers then being used However, when desirable it maybe stored as gas,or dissolved in water to form nitric' acid. The dilute acids resultingfrom thev NOzrecovery containing' salts dissolved therein may' befdischarged from the chamber during thev operation through val'ved lineigl'eading from the lower end of theV conical hopper 2D constituting thelower endv ofthe respective reaction chambers;

When the generation of"nitrogen peroxide from the nitrite has'beencompleted, the iiowof acid and airtofthez chamber is' discontinued byclosing the valves in the respective lines, the'valved connection Itisclosed and water i's'admittedl to the top of the tower throughlmanifold' 2 I and valved connection 22f`tolu'sh out any remainingsaitso'rV acids. Thereaftensteamm admitted to the' lower endl ot thetowerthrough manifold' 2'3 and valvedconn'ection 2li' toisteam out thetower and'thetower' is thend'ried by blowing'air therethrough the'manifold I`I and connection I2, the steamand airr being drawn from theupper en'd ofthe tower through valvedlconnection 25! A'fter the chambershave been washed, steamed and dried, following'the N62rec'overyoperation, the saddles', or' other gas' distributingdevices,are removed from` the chamber' through the openings 5 and may be admixedwith fresh chloritefor recharging the chamber;

While the nitrogen peroxide is being recovered from the nitrite` inchamber I1, chamber 2y may be used for the generationl ofA chlorinedioxide. Fina1ly,chamber 3 will be used'v for the generation-of chlorinedioxide, while the nitrogen peroxide is' being recovered from thenitrite inchamber'2 and chamber I is being'cleanedj. dried andrecharged. Thus, the operation may becarried on continuously withoutinterruption.

The several reaction chambers and the` connections thereto areidentical'andy like elements thereof are indicated by like referencenumerals on' the drawing. Each tower is' provided at its upper'endwithavperforat'edf partition 26 adapted to promote the separation of:suspendedl solids and' liquids from the eflluent'gases.

It will be appreciated that in thegeneratingand handling of chlorinedioxide; the concentration of the chlorine dioxide should generally be'less than that at which its partialpressure reaches '70 millimetersfofmercury. Usually the partial' pressure passed into the lower end of thechamber 5%?15 of' chlorine dioxide should' not exceed about 30 nitrogenperoxide prior to passing it to the chlorine dioxide generator or asuitable amount of air may separately be passed into the lower end ofthe chlorine dioxide generator concurrently with the passage of nitrogenperoxide thereto. The

amount of air premixed with the nitrogen peroxi ide is, with advantage,regulated by regulating the amount of excess air passed upwardly throughthe chamber during the nitrogen peroxide liberating step of the process.Where desired, additional air may subsequently be mixed with thenitrogen peroxide.

It will be appreciated that substantial amounts of nitrogen peroxideneed be supplied to the system only during the initial stage ofoperation and may be discontinued as soon as the step o1" recovering theNO2 from the nitrite is begun. Thereafter, all or substantially all ofthe NO2 requirement is recovered from the nitrite in my cyclic process.

I claim:

1. In the process for the generation of chlorine dioxide by reactingnitrogen peroxide with a chlorite of a metal of the class consisting ofthe alkali and alkaline earth metals resulting in the formation of thecorresponding nitrite, the steps of reacting a relatively non-volatileacid with the nitrite whereby a gas mixture of NO2 and NO is evolved,oxidizing the NO of the mixture to NO2 by admixing excess air therewithand reacting the NO2 with further chlorite to generate additionalchlorine dioxide.

2. A cyclic process Jfor the generation of chlorine dioxide whichcomprises reacting NO2 in dilution with air with a chlcrite of a metalof the class consisting of the alkali and alkaline earth metals bypassing the NO2 in contact with the chlorite whereby chlorine dioxideand a nitrite of the corresponding metal are formed, reacting thenitrite with a relatively non-volatile acid and thereby liberatingnitrogen peroxide and recycling the liberated nitrogen peroxide incontact with the chlorite to generate additional chlorine dioxide.

3. A cyclic process for the generation of chlorine dioxide whichcomprises passing nitrogen peroxide in contact with a chlorite of ametal of the class consisting of the alkali and alkaline earth metals,whereby chlorine dioxide is generated with the concurrent formation ofthe corresponding nitrite, reacting a relatively non-volatile acid withthe nitrite and thereby liberating a mixture of NO and NO2, oxidizingthe NO o1" the mixture to NO2 by mixing excess air therewith andrecycling the resultant NO2 diluted with the air in contact withadditional chlorite to generate further chlorine dioxide.

4. In the process for the generation of chlorine dioxide by reactingnitrogen peroxide with a chlorite of a metal of the class consisting ofthe alkali and alkaline earth metals resulting in the formation of thecorresponding nitrite, the steps of reacting suliuric acid with thenitrite whereby a gas mixture of NO2 and NO is evolved, oxidizing the NOof the mixture to NO2 by admixing excess air therewith and reacting theNO2 with further chlorite to generate additional chlorine dioxide.

5. A cyclic process for the generation of chlorine dioxide whichcomprises reacting NO2 in dilution with air with a chlorite of a metalof the class i consisting of the alkali and alkaline earth metals bypassing the NO2 in contact with the chlorite whereby chlorine dioxideand a nitrite of the corresponding metal are formed, reacting thenitrite with sulfuric acid and thereby liberating nitrogen peroxide andrecycling the liberated nitrogen peroxide in contact with the chloriteto generate additional chlorine dioxide.

6. A cyclic process for the generation of chlorine dioxide whichcomprises passing nitrogen peroxide in contact with a chlorite of ametal of the class consisting of the alkali and alkaline earth metals,whereby chlorine dioxide is generated with the concurrent formation ofthe corresponding nitrite, reacting sulfuric acid with the nitrite andthereby liberating a mixture of NO and NO2, oxidizing the NO of themixture to NO2 by mixing excess air therewith and recycling theresultant NO2 diluted with the air in contact with additional chloriteto generate further chlorine 1 dioxide.

WILLIS S. HUTCHINSON.

REFERENCES CITED The following references are of record in the le ofthis patent:

Mellor, Inorganic and Theoretical Chemistry, vol. 8, pp. 419, 429, 1928,Ed. Longmans, Green and Co., N. Y., publishers.

1. IN THE PROCESS FOR THE GENERATION OF CHLORINE DIOXIDE BY REACTINGNITROGEN PEROXIDE WITH A CHLORITE OF A METAL OF THE CLASS CONSISTING OFTHE ALKALI AND ALKALINE EARTH METALS RESULTING IN THE FORMATION OF THECORRESPONDING NITRITE, THE STEPS OF REACTING A RELATIVELY NON-VOLATILEACID WITH THE NITRITE WHEREBY A GAS MIXTURE OF NO2 AND NO IS EVOLVED,OXIDIZING THE NO OF THE MIXTURE IS NO2 BY ADMIXING EXCESS AIR THEREWITHAND REACTING THE NO2 WITH FURTHER CHLORITE TO GENERATE ADDITIONALCHLORINE DIOXIDE.